Yuu Suzukaze lost contact with his beloved childhood friend Karin Machihashi when they were young. Ten years later, she transfers into his high school class, and he is overjoyed at the reunion he has dreamed of. But his hopes for a simple, romantic school life are shattered when he discovers that Karin is no longer a single person—she has split into multiple distinct personalities, each with her own name, appearance, and traits. One is a shy, bookish introvert; another is a flashy, outgoing idol; a third is a narcissistic diva; and more emerge over time, including a chuunibyou and a doting type. All of them claim to be the real Karin, and all of them are in love with Yuu. The story follows Yuu as he navigates this absurd situation: a harem where every heroine is literally the same girl, forcing him to deal with a single childhood friend who has become many. Each new personality receives a focused narrative arc that explores her origin within Karin's psyche, deepens her bond with Yuu, and fuels comedic and heartfelt interactions. The overarching mystery is why Karin fractured in the first place, which builds toward a climactic revelation and a resolution in which Yuu must find a way to accept every facet of the girl he has always loved. The series balances romantic comedy with light emotional beats, set in a standard high school environment with typical school events such as festivals. The story proceeds through the introduction of each personality, culminating in a final volume that explains the cause of the split and brings Yuu’s relationship with all parts of Karin to a conclusive end.